For the first time, a team of scientists led by astronomers from Leiden University and the National Radio Astronomy Observatory has reliably detected “semi-heavy” water ice around a young star similar to the Sun. These results confirm the hypothesis that some of the water in our solar system was formed before the Sun and planets appeared.
The origin of “semi-heavy” water
The way astronomers track where water comes from is by measuring its deuterium ratio. This is the proportion of water that contains one atom of deuterium instead of one atom of hydrogen. Thus, instead of H2O, we get HDO, which is also called “semi-heavy” water. A high proportion of semi-heavy water is a sign that the water was formed in a very cold place, such as the primitive dark clouds of dust, ice, and gas that give birth to stars.
In Earth’s oceans, comets, and icy moons, up to one in several thousand water molecules consists of semi-heavy water. This is approximately ten times higher than expected based on the composition of the Sun. Therefore, astronomers have hypothesized that some of the water in the Solar System originated as ice in dark clouds hundreds of thousands of years before the birth of our Sun.
The origin of water
To confirm this hypothesis, astronomers needed to measure the deuterium ratio of water ice in star-forming regions. To do this, they used the James Webb Space Telescope (JWST). Its target was the protostar L1527 IRS.
L1527 IRS is located in the constellation Taurus, approximately 460 light-years from Earth. In a number of characteristics, it resembles the Sun at the time of its formation.
Prior to JWST, the ratio of water deuteration in star-forming regions could only be reliably measured in the gas phase, where it can undergo chemical changes. But thanks to the telescope’s sensitivity, astronomers were able to look “inside” and obtain a clear signature of semi-heavy water ice around the protostar.
The deuterium ratio of water in L1527 is very similar to that of some comets, as well as the protoplanetary disk of a more developed young star. This indicates a similar cold and ancient chemical origin of the water found in all these objects. The discovery is another piece of evidence that most water ice remains virtually unchanged from the earliest to the latest stages of star formation.
At the same time, the measured deuterium ratio of water ice in L1527 IRS is slightly higher than the ratios measured in some comets in the Solar System and water on Earth. This difference may be caused by various factors. For example, some of the water on comets and on Earth may have undergone chemical changes in the protoplanetary disk. Or perhaps the gas and dust cloud from which our Sun formed was different from the cloud in which L1527 IRS formed. Therefore, astronomers plan to conduct additional observations of semi-heavy water ice in the L1527 IRS system to investigate the possible causes of these differences.
According to Astronomie.nl
